Ethylene-vinyl acetate (EVA) copolymers are commercially important thermoplastic materials produced from ethylene and vinyl acetate. Transformation of EVA copolymers to other macromolecules can be readily achieved due to the potentially reactive acetoxy functionality. One of the most important transformations involves conversion of EVA copolymers to ethylene-vinyl alcohol (EVAL) copolymers. This transformation can go to completion or partial completion where the final product has both acetoxy and hydroxy moieties. As expected, such products possess needed properties different from their EVA copolymer precursors.
The transformation is typically accomplished by hydrolysis (reaction with water) or alcoholysis (reaction with an alcohol which is generally low boiling, e.g. methanol or ethanol). Furthermore, the reaction rate is enhanced greatly by the addition of a catalyst. Base catalysts are more preferred over acid catalysts. Many industrial processes use aqueous solutions of methanol and an alkaline catalyst (e.g. NaOH, KOH, NaOMe, LiOE.sup.+, etc.). The extent of the transformation is dictated by the process conditions.
After removal of the desired polymer, the alcohol used in the process is purified for reuse. The purification involves distilling the alcohol from the water and other components which have boiling points higher than the alcohol. This mixture also contains residual EVAL polymer which has a low water solubility. The removal of the alcohol results in the precipitation of the polymers in the distillation vessel. This is referred to as fouling. The precipitated EVAL polymer hinders the performance of the separation vessel and eventually the manufacturing process must be stopped to remove the precipitated polymer. Shutting down the manufacturing process to remove precipitated polymer is expensive and is preferably avoided. Accordingly, it would be advantageous to provide a method for preventing the precipitation of EVAL polymer in distillation vessels.